Expanding shoe mechanism



Aug. 29, 1939. H. B. MEAD 2,171,185

EXPANDING SHOE MECHANISM Filed June 2, 1938 2 Sheets-Sheet l @www Y Z755Aug. 29, 1939. H. B. MEAD 2,171,186

EXPANDING SHOE MECHANISM Filed June 2, 1938 '2 Sheets-Sheet 2 `PatentedAug. 29, 1939 UNiTED STATES EXPANDING SHOE MECHANISM Harold BertramMead, Ilford, England Application June 2, 1938, Serial No. 211,429 InGreat Britain June 3, 1937 Claims.

. This invention relates to expanding shoe mechanism particularly forbrakes, primarily but not exclusively for road Vehicles, of the kindwherein the brake shoes are movably mounted on a base 5 member and areexpanded to engage the surrounding drum by means of a cam mounted forrotation between their free ends. The mechanism is applicable also toautomatic clutches.

The object of the invention is to bring about automatically an increasedfrictional grip between shoes and drum by servo action in proportion tothe resistance offered by the drum. For example, in a brake, the brakingeffort is automatically increased, and in a clutch the pressure ofapplication is automatically increased.

According to the invention, an expanding shoe mechanism comprises adrum, a plurality of shoes movably mounted on a iioating base member anddisposed inside the drum for frictional engagement therewith, a camrotatably mounted on the base member for expanding the shoes, an anchorplate on which the floating base member is mounted to rock around theaxis of the brake against spring resistance, an auxiliary cam forincreasing the expansion of the shoes, and a connection between saidauxiliary cam and anchor plate whereby angular displacement between thefloating base member and anchor plate turns the auxiliary cam. f

Some embodiments of the vinvention will be described by Way of examplewith the aid of the accompanying drawings, wherein:

Figure l is a front elevation oi a brake showing a portion of the drumremoved on the section line I-I of Figure 2;

Figure 2 is a transverse vertical section through the middle of Figure l(showing cams and link, referred to later, in full);

Figure 3 is a rear face view according to Figure l;

Figures 4 and 5 are views similar to Figures l and 2 but of a modiedarrangement the section of Figure 4 being on IV-IV of Figure 5;

Figure 6 is a front elevation of an automatic clutch showing a portionof the drum removed on the section line V-VI of Figure '7; and

Figure 'l is a transverse vertical section through the middle of Figure6' (showing the cams, links, and centrifugal weights, referred to later,in full).

Referring t0 the drawings in general, the drum is designated l and theshoes 2; the latter are movably mounted (pivotally at 3 in Figures 1-5,and slidably in Figures 6-7) on the floating base 55.- member 4 and, asusual, are disposed inside the (ci. iss-7s) drum for frictionalengagement with the inner cylindrical surface when they are expanded bya main cam or cams 5 rotatably mounted on the iioating member il. Ananchor plate is designated 6, and the iioating plate t can rock aroundthe axis of the drum with respect to the anchor plate t against theresistance of springs iii.

In a convenient embodiment as shown in Figures 1 3 the auxiliary cam lis mounted or formed on a short link 3 rockable on pin 9 carried by thefixed anchor plate 6 which is coaxial with and adjacent to the floatingbase member The main cam 5 is fast with its axle l which is mounted forrotation in the oating plate l and the edge of the anchor plate is clearof this axle lil as shown, or may have an arcuate slot through which themain cam axle i9 passes. The axle carries at its end projecting from theanchor plate a cam operating arm i i, which is connected in any suitablemanner to brake levers and/or pedals. The axle is free to performangular movement around the brake axis together with the iioating plateThe auxiliary cam l is loose on the main cam axle ill and in thisembodiment is located between the main cam 5 and the floating plate et.This relativedisposition of cams 5 and l is reversed in Figures Ll and5. The pivot 9 for the link 8 carrying the auxiliary cam 'l' is xed inthe anchor plate 6 and passes through an arcuate slot l2'in the floatingplate i and the link is formed with an elongated hole i3 whereby it isloosely seated on the pivot 9.

The pivot 3 for the brake shoes is fixed in the floating plate i and isalso clear of the anchor plate 6.

Any suitable spring arrangement may be provided for resisting angularmovement of the oating plate li. In Figures 2, 3 and 5 will be seen apair of springs M anchored to the floating plate by one of therespective ends at l5, and to the anchor plate through the medium ofpivoted arms i6 mounted thereon. These arms I6 may be pulled againsttheir respective Stops l'i according to the direction of rotation of themember i in relation to the anchor plate 6', This willV put one of thesprings under tension to resist the relative movement of members l and6, Whilst the other spring and its arm l rides free in the compressiondirection.

In operation, when the brake shoes 2 are applied to the drum l by meansof the main cam 5 the floating plate i becomes connected to the drumthrough the main cam axle i9. If the momentum of the drum is sufficientto overcome the resisting action oi the respective spring I4 retainingthe floating plate same will be caused to perform angular movement andthe floating plate will cause the main cam axle l0 to be angularlydisplaced around the brake axis. The auxiliary cam 'I being looselymounted on the main cam axle Ill the latter will cause it to rocktherearound, owing to the pin and slot connection ifi-I3 of theauxiliary cam carrying link 8 with the anchor plate 6. Thus theauxiliary cam 'I will further expand the brake shoes in proportion tothe resistance of the drum to braking, the momentum of the brake drumbeing utilised for automatically increasing the braking effort; thisaction is illustrated in broken linesV where the cam centres move to theangle indicated by the line A-B.

In Figures 4 and 5 there is shown a modification wherein the chiefdifference is that the link I8 (equivalent to the link 8 of thepreviousembodiment) is located outside the drum, and on the other sideof the anchor plate 6. The auxiliary cam 'I is fast on a spindle I9which passes through the hollow axle 2U of the main cam 5. When there isrelative movement between the floating plate l and the anchor plate 6,as in the previous example, the spindle I9 is caused to turn (andconsequently the cam 1) through the me-V dium'of the crank arm 2l whichis pivoted to the link I8. This position is shown in dotted lines inFigure 4, the cam centres having moved through an angle bringing them onto the line A-B. Corresponding numerals of reference are given to otherparts corresponding in the other figures.

The applicability of the invention to an automatic clutch is seen inFigures 6 and '7. 'I'he anchor plate 6 may be assumed to be fixed to adriving shaft 22, and the drum I to a driven shaft 23. In this case theshoes 2 are applied to the drum when they are expanded by the main cams5 under the action of the weighted arms 24, these arms and their weights25 flying out centrifugally to rotate the cam axles when the mass insidethe drum is rotated anti-clockwise. It is to be understood that theanchor plate 6 and oating plate d are resiliently connected together bysprings or the like, e. g. as shown at I4, I6, Il in the previousembodiments, these springs not appearing in the sectional view Figure'7. Consequently rotation of the shaft 22 turns the plates 4 and 6, anddevices carried thereby, en bloc causing the shoes to expand asdescribed above. Then, as the resistance of the drum isV encountered,the floating plate I lags relatively to the plate 6, and through thelinks I8, crank arms I9 and auxiliary cams l, the shoes are furtherexpanded, augmenting the pressure of application between the clutchelements (i. e. shoes and drum respectively). It will be observed thatthe members I8, I9, 'I operate as in the brake design of Figures 4 and5, and are duplicated, as it is preferred to expand the shoes fromdiametrically opposite points, the shoes Z sliding on pin-and-Slotsupports 26.

I claim:

1. An expanding shoe mechanism comprising a drum, a plurality of shoesmovably mounted on a oating base member and disposed inside the drum forfrictional engagement therewith, a cam rotatably mounted on the basemember for expanding the shoes, an anchor plate on which the oating basemember is mounted to rock around the axis of the brake'against thespring resistance, an auxiliary cam for increasing the expansion of theshoes, and a link pivoted on the anchor plate by a pin-and-slotconnection, the pin passing through an arcuate slot in the oating plate,said link carrying the auxiliary cam, whereby angular displacementbetween the oating base member and the anchor plate rocks the link aboutits pivotal connection and turns the auxiliary cam.

2. An expanding shoe mechanism comprising a drum, a plurality of shoesmovably mounted on a oating base member and disposed inside the drum forfrictional engagement therewith, a cam rotatably mounted on the basemember for expanding the shoes, an anchor plate on which the floatingbase member is mounted to rock around the axis of the brake againstspring resistance, an auxiliary cam for increasing the expansion of theshoes, said auxiliary cam being carried by a spindle passing through ahollow axle revoluble in the floating base plate, the axle beingrotatable manually by a cam operating arm, and the spindle by a crankarm fixed thereto and pvoted to a link pivotally mounted on'the anchorplate, whereby angular displacement between the floating base member andanchor plate rocks the said link and crank arm and turns the auxiliarycam.

3. An expanding shoe mechanism comprising a drum, a plurality of shoesmovably mounted on a floating base member and disposed inside the drumfor frictional engagement therewith, a main cam rotatably mounted on thebase member for expanding the shoes, an anchor plate with respect towhich the floating base member is mounted to rock around the axis of thebrake against spring resistance, an auxiliary cam for increasing theexpansion of the shoes, the main cam being rotatable through centrifugalmeans, and a connection between said auxiliary cam and anchor platewhereby angular displacement between the floating base member and anchorplate turns the auxiliary cam.

4. An expanding shoe mechanism, comprising, a drum, shoes within thedrum, an anchor member, a oating base member carrying the expandingshoes and mounted to rotate relatively to said anchor member about anaxis concentric with the drum against which the shoes expand, a main camadapted to expan dthe shoes, an auxiliary cam mounted co-axially withthe main cam, means operated by movement of the oating base relativelyto the anchor member and operating the auxiliary cam to assist the maincam, and spring vmeans arranged to control the relative movement betweenthe floating base and the anchor member and tending to return thefloating base to a position in which the auxiliary cam releases theshoes. Y

- 5. An expanding shoe mechanism, comprising, a drum, an anchor plateand a base member all mounted in co-axial relation, said base memberbeing supported to rock relative to the anchor plate; a plurality ofshoes movably supported on the base member and disposed inside the drumfor frictional engagement therewith, a main cam rockably mounted on thebase member for expanding the shoes, an auxiliary cam mounted co-axiallywith the main cam on the base member for increasing the expansion of theshoes, a connection between said auxiliary cam and anchor plate wherebyangular displacement between the oating base member and the anchor plateturns the auxiliary cam, and means for normally and yieldingly holdingthe base member in fixed relation to the anchor plate.

6. An expanding shoe mechanism, comprising, a drum', an anchor plate anda base member all mounted in co-axial relation, and said base membersupported to rock relative to the anchor member, a plurality of shoesmovably supported on the base member and within the drum for frictionalengagement therewith, juxtaposed main and auxiliary cams co-axiallymounted on the base member for expanding the shoes, an operating arm foractuating the main cam, and link means for cperatively connecting theauxiliary cam with the anchor plate, said link means being locatedexteriorly of the drum.

'7. An expanding shoe mechanism, comprising, a drum, an anchor plate anda base member all mounted in co-axial relation, and said base memberbeing supported to rock relative to the anchor member, a plurality ofshoes movably mounted on the base member and disposed inside the drumfor frictional engagement therewith, main and auxiliary cams forexpanding the shoes, said main cam being mounted on a tubular axlemounted to rotate in the oating base member and said auxiliary cam beingmounted on a spindle arranged co-axially within said tubular axle, anoperating connection for said tubular axle, link means for connectingthe spindle of the main cam with the anchor plate, and spring meansarranged to control the relative movement between the floating base andthe anchor plate and tending to return the floating base to a positionin which the auxiliary cam releases the shoes.

8. An expanding shoe mechanism, comprising, a drum, an anchor plate anda base member all mounted in co-axial relation, and said base memberbeing supported to rock relative to the anchor member, a plurality ofshoes movably mounted on the base member and disposed inside the drumfor frictional engagement therewith, main and auxiliary cams forexpanding the shoes, said main cam being mounted on a tubular axlemounted to rotate in, the floating base member and said auxiliary cambeing mounted on a spindle arranged co-axally within said tubular axle,an operating connection for said tubular axle, link means for connectingthe spindle of the main cam with the anchor plate,

spaced abutments on the outer face of the anchor plate, arms pivoted atone end to the anchor plate, and. springs having their outer endsconnected to the free ends of said arms and their inner ends connectedto a portion of the floating base member, said springs controlling therelative movement between the floating base and the anchor plate andtending to return the floating base to a position in which the auxiliarycam releases the shoes.

9. An expanding shoe mechanism, comprising, a drum, an anchor plate anda base member all mounted in co-axial relation, said base member havinga. slot and being supported to rock relative tol the anchor plate, aplurality of shoes movably supported on the base member and disposedinside the drum for frictional engagement therewith, a spindle carriedby the base member, a main cam rockably mounted on the spindle forexpanding the shoes, an auxiliary cam loosely mounted on said spindleco-axially with the main cam for increasing the expansion of the shoes,a pivot pin carried by the anchor plate and projecting through the slotin the base member, a link carried with said auxiliary cam and having aslot receiving said pivot pin on the anchor plate whereby angulardisplacement between the floating base member and the anchor plate turnsthe auxiliary cam and means for normally and yieldingly holding the basemember in a fixed relation to the ancho-r plate.

An expanding shoe mechanism, comprising, a drum, expanding shoes, ananchor member and a base member all mounted in co-axial relation,co-axially mounted main and auxiliary cams for successively expandingsaid shoes against the drum, means for mounting said cams forindependent movement; pendulum means operated by centrifugal force,connected with and controlling the operation of the main cam; and aconnection between said auxiliary cam and the anchor member, wherebyangular displacement between the floating base member and the anchormember turns the auxiliary cam.

HAROLD BERTRAM MEAD.

